This week's Unsub probably had the worst case of self-esteem issues ever.
For what reason? It's possible that having your ex-wife say you're weak, you've always been weak doesn't inspire a lot of confidence.
To bolster his pride and his belief in his ability to protect their unborn child, he had to show he was strong - which he did by murdering anyone he saw as a threat to the tenants of the building in which he lived and worked.
In Criminal Minds Season 9 Episode 7 we caught up to Rossi and Reid having some drinks at Rossi's favorite dive... only to discover that the bar was closing for good.